Micromechanical sensors for measuring acceleration, rotational speed, and magnetic field are known and are produced in mass quantities for various automotive and consumer applications. Conventionally, for consumer applications the various sensed variables are still represented predominantly by separate sensor modules in the form of three-axis acceleration sensors, three-axis rotational speed sensors, and three-axis magnetic field sensors; however, there is a trend toward system integration, i.e., a realization of 6D elements as a compass module (measurements of acceleration and magnetic field), or IMU (Inertial Measurement Unit; measurements of acceleration and rotational speed), or 9D elements (measurements of acceleration and rotational speed and magnetic field).
In the existing art, standardly a plurality of chips for the various measured variables are installed in a plastic housing (e.g. LGA, BGA, QFN), as a so-called system-in-package (SiP). The named systems have differently separated chips that are functionally connected by a wired connection or via solder bumps.
Alternatively, MEMS and ASIC chips can be vertically integrated already at the wafer level. Here, vertical integration refers to the joining of MEMS and ASIC wafers as a composite, producing electrical contacts between the MEMS functional elements and the ASIC. Examples of vertical integration methods are discussed for example in U.S. Pat. Nos. 7,250,353 B2; 7,442,570 B2; US 2010 0109102 A1; US 2011 0049652 A1; US 2011 0012247 A1; US 2012 0049299 A1; and DE 10 2007 048604 A1.
In addition to plastic packagings, so-called “bare-die” systems are also known in which silicon chips are soldered onto the application circuit boards directly via solder bumps. Because these systems do not make use of plastic packaging, these sensors are distinguished by particularly small footprints. Bare-die designs of MEMS inertial sensors are known. In such conventional acceleration and rotational speed sensors, an ASIC, whose surface is significantly smaller than the surface of the MEMS element, is connected to the MEMS element via small solder bumps. The MEMS element includes a redistribution layer that enables a flexible wiring and that can be provided for external contacting with large solder bumps, whose height exceeds the ASIC thickness plus the thickness of the small solder bumps. A corresponding sensor device is described for example in US 2012 0119312 A1, in which each MEMS element is connected to an ASIC component and, depending on the existing size conditions, either the MEMS or the ASIC component is provided with external contacts.
For the magnetic sensor mechanism, various physical principles and measurement methods are used, such as resistive measurements of magnetoresistive layers (AMR, GMR), measurements of the inductance in soft-magnetic materials (flux gate or flip core design), or exploitation of the Hall effect. Many of the named technical solutions require an application of additional magnetic or magnetoresistive layers, thus increasing the complexity and costs of the production process. In particular, methods are standard in which the magnetic or magnetoresistive layers are applied directly on a CMOS-ASIC.
Increasingly, sensor modules are also being made “more intelligent,” meaning that a stronger pre-processing of the sensor data is carried out in order to calculate for example quaternions therefrom, and to give this already pre-processed information externally to the applications. For this process, additional microcontroller functionalities are required; here, microcontrollers can in principle be integrated into the sensor ASIC or can be used separately.